The present invention relates to Cochlear implant systems, and more particularly to a technique for programming a Cochlear implant system based, in part, on measured evoked potentials that precede the stapedius reflex.
One of the more perplexing problems facing users of Cochlear implant systems, and the clinicians and physicians who implant and adjust such systems, is properly setting the stimulation parameters used by these systems. That is, each Cochlear implant system must be adjusted to xe2x80x9cfitxe2x80x9d an individual patient, so that sounds are properly perceived by that patient, and so that sounds are not painfully too loud, or undetectably too soft, or otherwise not intelligible by the patient. This problem is especially difficult because heretofore so much of what is deemed a xe2x80x9cproperxe2x80x9d setting has been a subjective determination made by the patient. Ofttimes, however, due to the age or disabilities of the patient, the patient is ineffective at accurately communicating what he or she senses or xe2x80x9chearsxe2x80x9d through the implant system to the attending medical personnel. There is thus a need in the implantable Cochlear stimulation art for techniques, methods and systems for more objectively xe2x80x9cfittingxe2x80x9d the implant system to the individual patient.
Others have addressed this xe2x80x9cfittingxe2x80x9d problem in various ways. U.S. Pat. No. 5,626,629, for example, provides a clinician with various adjustment tools, including the use of a personal computer (PC) having a special software program loaded therein that help the clinician set and adjust numerous stimulation parameters.
Further techniques for objectively setting stimulation parameters involve the use of special electrodes and/or circuitry adapted to sense the stapedius reflex, as disclosed, e.g., in International Publication WO97/48447, published Dec. 12, 1997, filed in the Patent Cooperation Treaty (PCT) as International Application Number PCT/US97/10590, on Jun. 19, 1997. This PCT publication is incorporated herein by reference. Electrodes for more effectively sensing the stapedius reflex are disclosed in commonly-owned U.S. patent application Ser. No. 09/323,594, filed Jun. 6, 1999, now U.S. Pat. No. 6,208,882, also incorporated herein by reference.
While monitoring and sensing the stapedius reflex provides a valuable technique for obtaining objective feedback regarding sound loudness, which information in turn is useful in setting the stimulation parameters of an implantable Cochlear stimulation system, being able to accurately sense the stapedius reflex is not an easy task, and typically involves implantation of additional extra-Cochlear electrodes and additional sensing circuitry. There is thus a need for alternative ways, other than sensing the stapedius reflex, to obtain objective data that can aid in the setting of the stimulation parameters of a Cochlear stimulation device.
An evoked potential of probably myogenic origin is known to occur at a latency of about 5 to 12 milliseconds following acoustic stimulation. This evoked potential typically occurs between wave 5 of the elicited auditory brainstem response (EABR) and before mid-latency responses. This evoked potential is larger than EABRs, and occurs at high stimulation levels only. When taking EABR measurements, this evoked potential is generally considered an undesirable artifact, and its origin may not be fully understood at this time. It is likely that this evoked potential pre-empts the actual stapedius reflex. For purposes of this patent application, this evoked potential, occurring between wave 5 of the EABR at a latency of about 5 to 12 milliseconds following acoustic stimulation, is referred to as the xe2x80x9cmyogenic evoked responsexe2x80x9d or xe2x80x9cMERxe2x80x9d.
In the past, the MER has been measured with standard EABR electrodes, mounted at two different surface locations on the head. The MER has been measured for diagnostic purposes, i.e., for the purpose of objectively assessing functionality of the auditory nerve in response to electrical stimulation via a temporary needle electrode placed at the promontory or the round window niche. Such diagnostic application has been described by Nikos Marangos et al., of Hannover, Germany, in the early 1990""s.
The present invention addresses the above and other needs by measuring the described MER with permanently implanted electrodes that are connected to a Cochlear implant device. The measured MER is then used to assist in the objective programming and/or operation of the Cochlear implant.
Unlike the prior diagnostic measurements of the MER using surface electrodes mounted on the head, the MER is measured in accordance with the present invention between implanted electrodes, e.g., between two intra-Cochlear electrodes, between one intra-Cochlear electrode and one extra-Cochlear reference electrode, or between two extra-Cochlear electrodes.
Moreover, unlike prior techniques for obtaining objective data associated with an implant device, which have focused on measuring either the reflex response of the stapedial tendon or the neural potential on the facial nerve that feeds the stapedial tendon, the present invention does not measure the actual stapedius reflex. Hence, the present invention does not require electrodes to be placed into or in close proximity to the stapedial tendon, the stapes, or the facial nerve.
In accordance with one aspect of the invention, there is provided a method of objectively gathering stimulation data associated with programming an implantable cochlea stimulation (ICS) system. Such ICS system includes an implantable electrode array having at least intra-Cochlear electrode contacts, means for applying an electrical stimulus to a selected pair of the electrode contacts, and means for sensing an evoked potential occurring between a selected pair of the electrode contacts. The method includes the following steps: (a) selecting a pair of sensing electrodes through which the MER is to be sensed; (b) applying a stimulus of a selected energy or magnitude to the cochlea; (c) monitoring the selected sensing electrodes for the occurrence of the MER during a prescribed time period after application of the stimulus; (d) readjusting the energy or magnitude of the electrical stimulus as a function of whether the MER is sensed during the prescribed time period; (e) measuring the magnitude of the sensed MER; and (f) using the measured magnitude of the MER to generate data useful in programming the ICS system.
In accordance with another aspect of the invention, there is provided an improved system for objectively programming a Cochlear stimulation system. The Cochlear stimulation system includes an implantable Cochlear electrode array, means for selectively applying an electrical stimulus to selected electrode pairs within the electrode array, and means for sensing an evoked potential between selected electrode pairs within the electrode array. The improved system provided by the invention includes: (a) means for sensing and measuring an evoked response between a selected pair of electrode pairs during a prescribed time period following application of a stimulus; and (b) means for using the measured evoked response to assist in objective programming of the Cochlear stimulation system, and/or operation of the system. If used during operation, the measured evoked response may be used as a feedback signal to adjust the level of the stimuli to be applied by the Cochlear stimuli system, i.e., as a type of bionic automatic gain control (AGC) signal.
It is thus an object of the present invention to provide a method and system for obtaining objective data associated with setting stimulation parameters of a Cochlear implant system.
It is a feature of the invention to provide such a method and system that may be used without having to measure either the reflex response of the stapedial tendon or the neural potential on the facial nerve that feeds the stapedial tendon.
It is a further object of the invention to measure and constructively use an evoked response of myogenic origin, and a response which has heretofore been generally considered an undesirable artifact, to aid in the objective programming of a Cochlear implant system.